Book An Appointment



Leaky Gut and Leaky Brain: What’s the Link?


We’ve all had those moments when we just can’t think clearly.

Maybe we can’t focus. We’re forgetting things. Our mood may shift up and down erratically. We may even feel anxious and don’t understand why.

While these may be symptoms of cognitive impairment or changes to our mental state, they could also be due to hypothyroidism, chronic fatigue, hormonal changes, stress, and even a lack of sleep.

However, these neurological changes may also be due to the poor status of our gut microbiota – and poor gut microbiota may be more common than we think.

Gut microbiota consists of microorganisms that contribute to stabilizing our health and fighting diseases. Studies have linked a healthy gut function to the normal functioning of the central nervous system (CNS); in fact, microbiomes of the gastrointestinal tract help control very integral segments of our neurobiology, mental, behavioural, and overall health (including immune function, memory, depression, mood disruption, and anxiety). Abnormal behaviour and cognition may be connected to dysbiosis, which is when your microbial composition is disrupted from poor gut health.

Truly, there is ongoing communication between the gut and brain. And when this communication is disturbed, it can cause physical and physiological imbalances. This may happen when someone suffers from leaky gut syndrome.

Understanding Leaky Gut Syndrome and the Brain

Before we delve into leaky gut syndrome, let’s quickly understand the brain-gut communication, which is “bi-directional.” What this means is that when there’s stress on the brain (either physical or mental stress), this impacts the function of our gut. And when there’s disparity within the environment of our gut, this can cause changes in our behaviour or neurology, impacting the brain.

The gastrointestinal system houses its own nervous system called the enteric nervous system. It’s believed that within this system, combined with the vagus nerve and other pathways, the gut communicates with the brain.

The microorganisms in our intestines partake in nervous system health and function. Additionally, the digestive system helps protect your body from harmful substances. The walls of the intestines act as barriers, controlling what enters the bloodstream to be transported to other parts of the body for storage or further chemical change.

However, inflammation resulting from oxidative stress, and a diet low in fibre and high in sugar and saturated fats diet, may initiate this process; heavy alcohol use and excessive stress may also cause damage to the intestinal barrier. With that, the tight junctions between the epithelial cells that make up the intestinal wall open up. Substances that would normally stay in the intestine or become excreted by the body can cross into the inner layer of our intestinal wall and our bloodstream. And so the intestine becomes more permeable; it is “leaky” and bigger particles can pass through.

As a result, the immune system may be stimulated to release inflammatory mediators against these substances that are “crossing over”. These potentially unsafe substances include toxins, bacteria, and undigested particles from the food we’ve eaten. This process can trigger more inflammation and allergic responses, and further increase intestinal permeability; changes may result in our nervous system and possibly mood and behaviour malfunction.

People with leaky gut syndrome may experience pain in multiple joints, or chronic conditions such as those relating to the skin, diarrhea or abdominal pain, fatigue, depression, and/or body malaise. When leaky gut syndrome occurs, neurological changes may arise because your neurovasculature becomes compromised. As an essential component of the brain, the neurovasculature’s goal is to limit the blood-brain barrier absorbency; it counteracts harmful pathogens from entering the brain, where they trigger inflammation. This chronic inflammation can eventually lead to the loss of brain cells, which is why your neurovasculature must remain optimally healthy.

Hence, a dysfunction of the blood-brain barrier (also known as “leaky brain”) may be connected to various neurological conditions like low mood and anxiety. Studies are demonstrating that changes in gut microbiome composition may be associated with brain health, including anxiety and depression and certain neurological conditions.

Exploring Gut Microbiome and Health Conditions

Within the human gastrointestinal tract, the gut microbiota contains an ecosystem with trillions of microorganisms. This is primarily home to bacteria, but you’ll also find archaea, fungi, viruses and protozoa. Research has shown that gut microbiome may impact the physiology of its “human host”, which includes regulating immunity and metabolic homeostasis.

The microorganisms influence the progression of chronic diseases, such as gastrointestinal and metabolic disorders. When you metabolize tryptophan, an essential amino acid, this is also mediated by your gut microbiome; in turn, your gut microbiome may modulate serotonin, the neurotransmitter known for inducing a sense of happiness. (In fact, gut microbes also synthesize GABA, dopamine, acetylcholine and noradrenaline.) This is where you’ll find an interaction between brain-gut microbiota. Let’s consider this interaction to see how gut health may play a role in a few health conditions:

Serotonin, Depression and Anxiety:

Did you know that the highest amount of serotonin is located in the gut? Serotonin participates in regulating pain perception, as well as gastrointestinal secretion and motility. In fact, gut microorganisms can generate serotonin and modulate serotonin biosynthesis. Serotonin has many responsibilities, including adapting your mood, sleep, memory, sexual cravings, and such. Those with leaky gut syndrome may produce less serotonin in the gut, which has shown to contribute to conditions associated with low serotonin levels (i.e. depression and anxiety).

Dopamine and Parkinson’s Disease:

Increased gut permeability and gut microbiota changes are being studied as a contributing cause, pathway and treatment of diseases of the nervous system, including Parkinson disease (PD). It’s been postulated that the presynaptic neuronal protein, called alpha-synuclein, malfunctions and is linked to PD. Studies have suggested that this protein travels from the gut, through the vagus nerve and to the brain, physically misfolding and transmitting its unusual shape onto normal variants of the same protein. (FYI: gastrointestinal symptoms (i.e. constipation), leaky gut syndrome and distorted gut microbiota have been present for several years in PD patients before the condition’s clinical onset).

Studies have also shown a correlation between increased intestinal permeability and intestinal alpha-synuclein (a known PD precursor), implying a likely link between inflammation and leaky gut in the development of PD. Alpha-synuclein deposition plays an imperative role in the neurodegenerative process because this specific protein deposition causes toxicity to the neurons.

Parkinson’s is instigated by the death of dopaminergic neurons, which begins when there’s an alpha-synucleian disruption to cellular functions. These “disruptions” occur in brain regions related to coordinating movement. Signals that are propelled down the spinal cord are key for regulating muscle contraction; but when there is damage to this part of the brain, signalling is compromised and may trigger the physical symptoms of PD (i.e. tremors on one hand, stiffness). Dopamine production, especially in the gut, is thought to be disrupted by the alpha-synuclein deposition; this is why restoring gut microbiome may modify the neurodegenerative process of Parkinson’s.

Causes of Leaky Gut Syndrome

As we mentioned, dysbiosis (or poor gut health) is a contributing factor behind leaky gut syndrome. The gut holds countless bacteria, and when the balance between beneficial and harmful bacteria is interrupted, it can disturb the functioning of the intestinal wall’s barrier. The following are other likely contributing factors to leaky gut syndrome:

  • Excessive sugar intake: an unhealthy diet high in sugar, especially fructose, can harm the barrier function of the intestinal wall.
  • Non-steroidal anti-inflammatory drugs (NSAIDS): in particular, using NSAIDs (i.e. ibuprofen) on a long-term basis can increase intestinal absorbency.
  • Excessively drinking alcoholic beverages: can increase intestinal permeability.
  • Nutrient deficiencies: deficiencies in vitamin A, vitamin D and zinc have been related to increased intestinal permeability.
  • Inflammation: a disturbed gut lining can trigger inflammation and alter the normal bacteria in your gut.
  • Stress: chronic stress may be behind many gastrointestinal disorders, including leaky gut.
  • Yeast overgrowth: yeast is naturally found in the gut, but too much yeast may cause leaky gut syndrome.
  • Celiac disease: gliadin, a protein component of gluten, may jeopardize gut structure.


How Can You Improve Gut Health?

There are some ways you can help your body reach optimal gut health. For instance, your diet choices can increase or decrease the microbiota diversity in the gut. According to a Dutch study of 1135 participants, researchers identified links between various gut microbiota levels (i.e. symbiotic, pathogenic) with 126 environmental factors. Diet, disease, and the use of medication were some of the environmental factors related to gut microbiota levels. The measurement of microbiota diversity decreased when participants ate high amounts of carbohydrates, sugary drinks, beer, bread, savoury snacks, and, to a minor extent, high fat consumption, dry seeds, and legumes. In the study, gut microorganism diversity was also lessened in individuals who reportedly had irritable bowel syndrome (IBS) and used antibiotics.

However, microbial diversity augmented when study participants had more coffee, fruit, vegetables, and red wine; tea and eating breakfast were also shown to improve microbial diversity. Drinking red wine was related to a high amount of microbiota that are known to be anti-inflammatory. This is understandable, as red wine, coffee, and tea, are high in polyphenols, which are compounds that help increase prebiotics (a type of fiber that helps support a healthy gut) and promote the growth of beneficial bacteria.

Bottom line: consider increasing your fibre intake and eat high-fibre fruits and vegetables. Opt for foods and drinks with high levels of polyphenols (i.e. hazelnuts, berries, grapes, dark chocolate, raw cocoa, red wine, and coffee). Note: one glass of wine or one cup of coffee per day may suffice for optimal gut health.

You May Also Try These Tips to Improve Gut Health

  1. Remove inflammation triggers to help rebuild gut health (i.e. reduce your sugar intake, identify food sensitivities, treat yeast overgrowth, etc.). Refraining from the following may also positively effect gut microbiota: high amounts of carbohydrates, sugary drinks, beer, bread, savoury snacks, dry seeds, and legumes and excessive use of antibiotics.
  2. Discuss nutraceutical support with your health care provider to help rebuild your digestive health. This may contribute to correcting any nutritional deficiencies while enhancing gut health.
  3. Consider supplementing with prebiotics / probiotics. These have the ability to restore normal microbial balance and may have potential in treating/preventing anxiety and depression.
  4. Eat more fermented foods because they will help promote healthy bacteria in your gut. Natural sources of fermented foods include yogurt, kefir, or sauerkraut, kimchi, miso and tempeh.
  5. 5. De-stress yourself. If stress is causing poor digestion, make sure you get regular physical activity, such as walking and/or running. Yoga, which focuses on alignment and posture, may also alleviate gastrointestinal symptoms and alleviate stress.
  6. Remove pathogens. Pathogens can create intestinal discomfort and increase gutpermeability. Pathogens can harm your intestinal health and disrupt gut structure, too. With that, ask your health care provider about being tested for identifying and eliminating pathogens. Stool testing may also provide insight into the microogranisms of your gut, which may help evaluate the status of beneficial and pathogenic microorganisms in your gut (i.e. bacteria, parasites and yeast.)


Harnessing Optimal Gut Health

As we’ve learned, the gut and brain effectively correspond through pathways via bi-directional communication. When there is an imbalance with this communication, gastrointestinal and mental obstacles may occur. Research is showing that maintaining a healthy gut may be a way to achieve both physical and mental wellness.

If you want to improve your gut health, our naturopathic doctor can create a program that caters to your health needs only. The Toronto Functional Medicine Centre will conduct a complete functional medicine evaluation; proactive lab testing may be required to help determine a specific diet and lifestyle modification (i.e. removing food sensitivities). A treatment plan can be created to help remove toxins and pathogenic microorganisms, while supporting gut and brain health. Ready to get started? Phone our clinic at (416) 968-6961 or click here to book your appointment.



Mireia Valles-Colomer ; Gwen Falony; Youssef Darzi; Ett jeF.Tigchelaar; JunWang  Raul Y. it; Carmen Schiweck, Alexander Kurilshikov, Marie joossens;  Cisca Wijmenga; Stephan Claes; Lukas Van Oudenhove; Alexandra; hernakova, Sara Vieira-Silva; and Jeroen Raes The neuroactive potential of the human gut microbiota in quality of life and depression

Serotonin, tryptophan metabolism and the brain–gut–microbiome axis SM O’Mahony, G Clarke, YE Borre, TG Dinan, JF Cryan Behav. Brain. Res., 2015

Emily Fitzgerald, Sarah Murphy, Holly A. Martinson-Alpha-Synuclein Pathology and the Role of the Microbiota in Parkinson’s Disease Front Neurosci. 2019; 13: 369. Published online 2019 Apr 24. doi: 10.3389/fnins.2019.00369 PMCID: PMC6491838

Lyte, M. & Cryan, J. F. (eds) Microbial Endocrinology: Interkingdom Signaling in Infectious Disease and Health (Springer, New York, 2014)

Goldstein, D. S., Holmes, C., Lopez, G. J., Wu, T. & Sharabi, Y. Cerebrospinal fluid biomarkers of central dopamine deficiency predict Parkinson’s disease. Parkinsonism Relat. Disord. 50, 108–112 (2018).

Obrenovich M., Sankar Chittoor Mana T., Rai H., Shola D., Christopher S., McCloskey B., Levison B.S. Recent findings within the microbiota-gut-brain-endocrine metabolic interactome. Pathol. Lab. Med. Int. 2017;9:21–30. doi: 10.2147/PLMI.S121487. 

S.R. Gill, M. Pop, R.T. Deboy, P.B. Eckburg, P.J. Turnbaugh, B.S. Samuel, et al. Metagenomic analysis of the human distal gut microbiome Science, 312 (2006), pp. 1355-1359

Ronald D. Hills, Jr., Benjamin A. Pontefract, Hillary R. Mishcon, Cody A. Black, Steven C. Sutton, Cory R. Theberge-Gut Microbiome: Profound Implications for Diet and Disease Nutrients. 2019 Jul; 11(7): 1613. Published online 2019 Jul 16. doi: 10.3390/nu11071613

E.A. Franzosa, X.C. Morgan, N. Segata, L. Waldron, J. Reyes, A.M. Earl, et al. Relating the metatranscriptome and metagenome of the human gut Proc Natl Acad Sci USA, 111 (2014), pp. E2329-E2338

R.E. Ley, C.A. Lozupone, M. Hamady, R. Knight, J.I. Gordon Worlds within worlds: evolution of the vertebrate gut microbiota Nat Rev Microbiol, 6 (2008), pp. 776-788

Clarke G, Stilling RM, Kennedy PJ, Stanton C, Cryan JF, Dinan TG. 2014. Annual Review of Pharmacology and Toxicology Vol. 60:477-502 (Volume publication date January 2020)

Obrenovich M., Rai H., Chittoor Mana T.S., Shola D., McCloskey B., Sass C., Levison B. Dietary co-metabolism within the microbiota-gut-brain-endocrine metabolic interactome. BAO Microbiol. 2007;2:022. 

Siniscalco D., Schultz S., Brigida A.L., Antonucci N. Inflammation and neuro-immune dysregulations in autism spectrum disorders. Pharmaceuticals. 2018;11:56. doi: 10.3390/ph11020056. 

Main B.S., Minter M.R. Microbial immuno-communication in neurodegenerative diseases. Front. Neurosci. 2017;11:151. doi: 10.3389/fnins.2017.00151. 

Lanza G., Bella R., Cantone M., Pennisi G., Ferri R., Pennisi M. Cognitive impairment and celiac disease: Is transcranial magnetic stimulation a trait d’union between gut and brain? Int. J. Mol. Sci. 2018;19:2243. doi: 10.3390/ijms19082243. 

Bella R., Lanza G., Cantone M., Giuffrida S., Puglisi V., Vinciguerra L., Pennisi M., Ricceri R., D’Agate C.C., Malaguarnerae G. Effect of a gluten-free diet on cortical excitability in adults with celiac disease. PLoS ONE. 2015;10:e0129218. doi: 10.1371/journal.pone.0129218. 

Maes M., Kubera M., Leunis J. The gut-brain barrier in major depression: Intestinal mucosal dysfunction with an increased translocation of LPS from gram negative enterobacteria (leaky gut) plays a role in the inflammatory pathophysiology of depression. Neuro Endocrinol. Lett. 2008;29:11

González-Arancibia C1,2,3, Urrutia-Piñones J1,3, Illanes-González J1,3, Martinez-Pinto J2, Sotomayor-Zárate R2, Julio-Pieper M1, Bravo JA4. Do your gut microbes affect your brain dopamine?  Psychopharmacology (Berl). 2019 May;236(5):1611-1622. doi: 10.1007/s00213-019-05265-5. Epub 2019 May 17

by L Galland – ‎2014 – ‎Cited by 276 – ‎Related articles The progress of gut microbiome research related to brain disorders; › pmc › articles ›PMC4259177

Ronald D. Hills, Jr.,1,* Benjamin A. Pontefract,2,3 Hillary R. Mishcon,1 Cody A. Black,1,4 Steven C. Sutton,1 and Cory R. Theberge; Nutrients. Gut Microbiome: Profound Implications for Diet and Disease; 2019 Jul; 11(7): 1613.Published online 2019 Jul 16. doi: 10.3390/nu11071613 PMCID: PMC6682904; PMID: 31315227

Dutta SK, Verma S, Jain V, et al. Parkinson’s Disease: The Emerging Role of Gut Dysbiosis, Antibiotics, Probiotics, and Fecal Microbiota Transplantation. J Neurogastroenterol Motil. 2019;25(3):363‐376. doi:10.5056/jnm19044

 Forsyth CB, Shannon KM, Kordower JH, et al. Increased intestinal permeability correlates with sigmoid mucosa alpha-synuclein staining and endotoxin exposure markers in early Parkinson’s disease. PLoS One. 2011;6:e28032. doi: 10.1371/journal.pone.0028032. 

Braak H, de Vos RA, Bohl J, Del Tredici K. Gastric alpha-synuclein immunoreactive inclusions in Meissner’s and Auerbach’s plexuses in cases staged for Parkinson’s disease-related brain pathology.Neurosci Lett. 2006;396:67–72. doi: 10.1016/j.neulet.2005.11.012. 

Braak H, Del Tredici K. Potential pathways of abnormal tau and α-synuclein dissemination in sporadic Alzheimer’s and Parkinson’s diseases. Cold Spring Harb Perspect Biol. doi: 10.1101/cshperspect.a023630. Published Online First: 31 Aug 2016

Leonidas Stefanis Laboratory of Neurodegenerative Diseases, Biomedical Research Foundation of the Academy of Athens, and Second Dep – / on May 3, 2020 – Published by Cold Spring Harbor Laboratory Press: May 03, 2020

Franzosa, EA, Huang, K, Meadow, JF, et al. Identifying personal microbiomes using metagenomic codes. Proc Natl Acad Sci USA. 2015, 112(22): E2930–E2938.

Scheperjans, F, Aho, V, Pereira, PA, et al. Gut microbiota are related to Parkinson’s disease and clinical phenotype. Mov Disord. 2015, 30(3): 350–358.

Unger, MM, Spiegel, J, Dillmann, KU, et al. Short chain fatty acids and gut microbiota differ between patients with Parkinson’s disease and age-matched controls. Parkinsonism Relat Disord. 2016, 32: 66–72.

Fasano, A, Bove, F, Gabrielli, M, et al. The role of small intestinal bacterial overgrowth in Parkinson’s disease. Mov Disord. 2013, 28(9): 1241–1249.

Tan, AH, Mahadeva, S, Thalha, AM, et al. Small intestinal bacterial overgrowth in Parkinson’s disease. Parkinsonism Relat Disord. 2014, 20(5): 535–540.

Lee, WY, Yoon, WT, Shin, HY, et al. Helicobacter pylori infection and motor fluctuations in patients with Parkinson’s disease. Mov Disord. 2008, 23(12): 1696–1700.


CALL US TODAY (416) 968-6961